mapping problem ... crud operations

gistfile1.m

 RKObjectMapping* channelMapping = [RKObjectMapping mappingForClass:[Channel class]];
  
  // Core data
  //channelMapping.primaryKeyAttribute = "channelID";
  // For now using NSObject derived thing  

  [channelMapping mapKeyPathsToAttributes:
     @"id",          @"channelID",
     @"created_at",  @"createdAt",
     @"updated_at",  @"updatedAt",
     @"name",        @"name",
     @"description", @"description",
     @"public",      @"isPublic",
      nil]; 

  [serializationChannelMapping mapKeyPathsToAttributes:
   @"name",        @"name",
   @"description", @"description",
   @"public",      @"isPublic",
   nil]; 

  [objectManager.mappingProvider setSerializationMapping:serializationChannelMapping forClass:[Channel class]];


  [objectManager.mappingProvider setMapping:channelMapping forKeyPath:@"channels"];
  // [objectManager.mappingProvider registerMapping:channelMapping withRootKeyPath:@"channel"];
  [objectManager.router routeClass:[Channel class] toResourcePath:@"channels" forMethod:RKRequestMethodPOST];
  [objectManager.router routeClass:[Channel class] toResourcePath:@"channels/(channelID)" forMethod:RKRequestMethodGET];
  [objectManager.router routeClass:[Channel class] toResourcePath:@"channels/(channelID)" forMethod:RKRequestMethodDELETE];
  [objectManager.router routeClass:[Channel class] toResourcePath:@"channels/(channelID)" forMethod:RKRequestMethodPUT];

when I try to POST a new one I get

2011-08-09 14:24:23.895 TestApp[31268:207] D restkit.network:RKRequest.m:257 Sending asynchronous POST request to URL http://localhost:3000/api/v1/channels.
2011-08-09 14:24:23.895 TestApp[31268:207] D restkit.network:RKObjectLoader.m:290 POST or PUT request for source object test description, serializing to MIME Type application/json for transport...
2011-08-09 14:24:23.895 TestApp[31268:207] D restkit.object_mapping:RKObjectMappingOperation.m:428 Starting mapping operation...
2011-08-09 14:24:23.896 TestApp[31268:207] D restkit.object_mapping:RKObjectMappingOperation.m:434 Finished mapping operation successfully...
2011-08-09 14:24:23.896 TestApp[31268:207] D restkit.network.queue:RKRequestQueue.m:187 Sent request <RKObjectLoader: 0x65d0b60> from queue <RKRequestQueue: 0x6370190>. Loading count = 1 of 5
2011-08-09 14:24:24.706 TestApp[31268:207] D restkit.network:RKResponse.m:182 NSHTTPURLResponse Status Code: 422
2011-08-09 14:24:24.707 TestApp[31268:207] D restkit.network:RKResponse.m:183 Headers: {
"Cache-Control" = "no-cache";
Connection = "Keep-Alive";
"Content-Length" = 27;
"Content-Type" = "application/json; charset=utf-8";
Date = "Tue, 09 Aug 2011 21:24:24 GMT";
Location = "http://localhost:3000/api/v1/channels";
Server = "WEBrick/1.3.1 (Ruby/1.9.2/2010-12-25)";
"X-Runtime" = "0.791108";
"X-Ua-Compatible" = "IE=Edge";
}
2011-08-09 14:24:24.707 TestApp[31268:207] D restkit.object_mapping:RKObjectMapper.m:240 Performing object mapping sourceObject: {
name = (
"can't be blank"
);
}
and targetObject: (null)
2011-08-09 14:24:24.707 TestApp[31268:207] D restkit.object_mapping:RKObjectMapper.m:264 Found unmappable value at keyPath: errors
2011-08-09 14:24:24.708 TestApp[31268:207] D restkit.object_mapping:RKObjectMapper.m:264 Found unmappable value at keyPath: channels
2011-08-09 14:24:24.708 TestApp[31268:207] D restkit.object_mapping:RKObjectMapper.m:264 Found unmappable value at keyPath: error
2011-08-09 14:24:24.708 TestApp[31268:207] W restkit.object_mapping:RKObjectMapper.m:60 Adding mapping error: Could not find an object mapping for keyPath: ''
2011-08-09 14:24:24.708 TestApp[31268:207] E restkit.network:RKObjectLoader.m:178 Encountered errors during mapping: Could not find an object mapping for keyPath: ''
2011-08-09 14:24:24.708 TestApp[31268:207] E restkit.network:RKObjectLoader.m:277 Encountered an error while attempting to map server side errors from payload: Could not find an object mapping for keyPath: ''
2011-08-09 14:24:24.709 TestApp[31268:207] TestApp Payload: {"name":["can't be blank"]}
2011-08-09 14:24:24.709 TestApp[31268:207] Error: Could not find an object mapping for keyPath: ''
2011-08-09 14:24:24.709 TestApp[31268:207] D restkit.network.queue:RKRequestQueue.m:368 Request <RKObjectLoader: 0x65d0b60> failed loading in queue <RKRequestQueue: 0x6370190> with error: Could not find an object mapping for keyPath: ''.(Now loading 0 of 5)